1. Field of the Invention
This invention relates to a variable displacement compressor and a displacement control valve for the variable displacement compressor, and more particularly to a variable displacement compressor for compressing a refrigerant gas in a refrigeration cycle for an automotive air conditioner, and a displacement control valve for a variable displacement compressor, for use therein.
2. Description of the Related Art
A compressor used for compressing refrigerant in a refrigeration cycle for an automotive air conditioner is driven by an engine, and hence is not capable of controlling the rotational speed thereof. For this reason, a variable displacement compressor capable of changing the compression displacement for compressing refrigerant is employed so as to obtain adequate refrigerating displacement without being constrained by the rotational speed of the engine.
In the above-mentioned variable displacement compressor, compression pistons are connected to a wobble plate fitted on a shaft driven for rotation by the engine, and the angle of the wobble plate is changed to change the length of piston stroke for changing the delivery quantity of the compressor.
The angle of the wobble plate is continuously changed by introducing part of the compressed refrigerant into a gastight pressure-regulating chamber and changing the pressure of the introduced refrigerant, thereby changing a balance between pressures applied to the opposite sides of each piston.
A compression displacement control device disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 2001-132650 has a solenoid control valve arranged between a discharge port and a pressure-regulating chamber of a compressor or between the discharge port and a suction port of the same. This solenoid control valve opens and closes the communication such that a differential pressure across the solenoid control valve is maintained at a predetermined value. The predetermined value of the differential pressure can be set from outside by a current value. As a result, when the engine rotational speed increases, the pressure introduced into the pressure-regulating chamber is increased to reduce the displacement for compression, and when the engine rotational speed decreases, the pressure introduced into the pressure-regulating chamber is reduced to increase the displacement for compression, whereby the pressure of refrigerant discharged from the compressor is maintained at a constant level.
Although refrigerant generally used in a refrigeration cycle of an automotive air conditioner is a chlorofluorocarbon alternative HFC-134a, there has recently been developed a refrigeration cycle which causes the refrigerant to perform refrigeration in a supercritical region where the temperature of the refrigerant is above its critical temperature, e.g. a refrigeration cycle using carbon dioxide as refrigerant
In the conventional solenoid control valve for the compression displacement control device, to minimize operating displacement of the variable displacement compressor, it is required to maximize the amount of refrigerant introduced into the pressure-regulating chamber, but if the size of the valve is small, the amount of refrigerant introduced is small, and hence transition to a minimum displacement operation takes time, which can degrade controllability of the compressor.
On the other hand, when the size of the valve is increased so as to increase the amount of refrigerant introduced, the pressure-receiving area of the valve is also increased, and hence a large solenoid force is required to control the valve. Particularly in the refrigeration cycle using carbon dioxide as the refrigerant, since the pressure of refrigerant is increased to the supercritical region, the discharge pressure of the refrigerant becomes very high, so that the solenoid force for controlling the valve is also increased. This requires a huge solenoid, which causes an increase in the size of the solenoid valve and a resultant increase in manufacturing costs.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a variable displacement compressor and a displacement control valve for the variable displacement compressor which are capable of performing transition between operating capacities in a reduced time period and operating without using a large solenoid force even when the size of the valve is increased so as to increase the amount of refrigerant.
In order to accomplish the above object, a variable displacement compressor including a wobble member arranged in a pressure-regulating chamber formed airtightly, such that an inclination angle of the wobble member can be changed with respect to a rotational shaft, and driven by rotation of the rotational shaft for wobbling motion, and pistons each connected to the wobble member for performing reciprocating motion in a direction parallel to the rotational shaft in accordance with the wobbling motion of the wobble member, to thereby draw refrigerant from a suction chamber into a cylinder, compress the refrigerant, and deliver the compressed refrigerant from the cylinder to a discharge chamber is provided. The variable displacement compressor is characterized in that a flow rate of the refrigerant flowing in a first refrigerant passage extending from the discharge chamber to the pressure-regulating chamber and a flow rate of the refrigerant flowing in a second refrigerant passage extending from the pressure-regulating chamber to the suction chamber are controlled in an interlocked fashion such that the first refrigerant passage and the second refrigerant passage are opened and closed, based on a change in a differential pressure between pressure in the suction chamber and pressure in the discharge chamber.
In addition, in order to accomplish the above object a displacement control valve for a variable displacement compressor, for controlling an amount of refrigerant introduced from a discharge chamber into a pressure-regulating chamber, such that a differential pressure between pressure in the suction chamber and pressure in the discharge chamber are maintained at a predetermined differential pressure, to thereby change an amount of the refrigerant discharged from the variable displacement compressor is provided. The displacement control valve for a variable displacement compressor is characterized by comprising the steps of: (a) first and second valve elements operated in an interlocked fashion for opening and closing a refrigerant passage extending between the discharge chamber and the pressure-regulating chamber and a refrigerant passage extending between the pressure-regulating chamber and the suction chamber, respectively; (b) a solenoid section for applying a solenoid force corresponding to the predetermined differential pressure to the first and second valve elements.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.